Method and apparatus for tuning a PID controller

A method of tuning a controller for a process in a feedback control system comprising the steps of:

• (a) bringing the system into asymmetric self-excited oscillations (further referred to as asymmetric relay feedback test) via the introduction into the system an element having a nonlinear characteristic in series with the process, and applying a constant set point signal ƒ0 to the system, so that the error signal is the difference between the set point and the process output signal, the error signal is an input of the nonlinear element, and the output of the nonlinear element is a control signal for the process;
• (b) measurement of the frequency of the oscillations Ω, average (over the period of the oscillations) value of the process output signal y0, and average (over the period of the oscillations) control signal u0;
• (c) choosing the process model, parameters of which have unknown values;
• (d) identification of the parameters of the process model with the measurements obtained;
• (e) tuning the controller in dependence on the identified parameters of the process model.